1. Technical Field
The present application relates to a hydraulic expansion chuck for chucking a tool, in particular a boring tool or milling cutter.
2. Background Information
An expansion chuck is used to connect a tool that is driven in rotation with the drive spindle of a machine tool. For this purpose an expansion chuck has a pronounced expansion chuck axis around which the expansion chuck and the tool clamped in it are driven in rotation. In the direction of this expansion chuck axis, an expansion chuck always has a tool-side end which is provided to hold the tool, and a machine-side end, which is realized so that it forms a connection between the expansion chuck and the drive spindle of the machine tool. Hydraulic expansion chucks form a genre of expansion chucks that is described in the prior art. On an expansion chuck of this type, the receptacle for the tool is formed by a thin-walled expansion bushing. The expansion bushing is surrounded by a pressure chamber which is filled with a pressure fluid, such as an oil, for example. The expansion chuck is then realized so that when pressure is applied to the pressure fluid, the expansion bushing is elastically deformed radially and thereby chucks the tool that is being used in place. One of the advantages of a hydraulic expansion chuck is that in operation, it damps any vibrations and impacts that occur. This property makes it possible to achieve a particularly high surface quality during the machining and a long useful life of the tool.
WO 03/095132 A1 describes a hydraulic expansion chuck of this type. On this expansion chuck of the prior art, the pressure chamber is realized between an expansion bushing which is realized in one piece with a base body and a chucking ring which is screwed onto the base body. By screwing or unscrewing the chucking ring with respect to the base body, the volume of the pressure chamber can thereby be reduced or increased, and the pressure fluid can thereby be pressurized or depressurized.
In contrast to the chuck described above, on an expansion chuck there is frequently a pressure generating unit, e.g. on that is realized in the form of a piston-cylinder unit, which is axially offset toward the tool-side end with respect to the pressure chamber and the expansion bushing. An expansion chuck of this type is described in WO 98/39123 A1, for example. For the transmission of the pressure from the pressure generating device into the pressure chamber, on this expansion chuck an oil conducting system is provided, which consists of narrow connecting borings that are introduced into the material of which the expansion chuck is made.
An expansion chuck which is pushed onto a drive shaft with an expansion bushing that can chuck both radially outwardly and radially inwardly is also known from German Patent No. 743 530 C.
In particular in mold and die construction, very long and narrow expansion chucks are required. Conventional expansion chucks, however, can no longer be constructed in such long and narrow designs or only with considerable expense and at considerable effort. For example, on a particularly narrow expansion chuck a movable chucking ring, e.g. of the type described in WO 03/095132 A1, can no longer be installed for space reasons. Likewise a connecting boring, e.g. of the type described in WO 98/39123 A1 to transmit the pressure, can no longer be used on account of the thin walls of a narrow expansion chuck or can only be realized with a great deal of effort. As the length of the expansion chuck increases, the technical effort required to introduce a correspondingly longer connecting boring also increases drastically. An additional problem results from the fact that, when pressure is applied, stresses are introduced into the material of the expansion chuck also in the vicinity of each connecting boring, which can lead to a significant bending of the expansion chuck and thus have an adverse effect on the true or concentric running of the tool.